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PYSEC-2026-2046

Werkzeug safe_join() allows Windows special device names

Details

Werkzeug's `safe_join` function allows path segments with Windows device names. On Windows, there are special device names such as `CON`, `AUX`, etc that are implicitly present and readable in every directory. `send_from_directory` uses `safe_join` to safely serve files at user-specified paths under a directory. If the application is running on Windows, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely.

Are you affected?

Enter the version of the package you're using.

Affected packages

PyPI / werkzeug

Introduced in: 0 Fixed in: 3.1.4

Fix pip install --upgrade 'werkzeug>=3.1.4'

References

https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2 [WEB]
https://nvd.nist.gov/vuln/detail/CVE-2025-66221 [ADVISORY]
https://github.com/pallets/werkzeug/commit/4b833376a45c323a189cd11d2362bcffdb1c0c13 [WEB]
https://github.com/pallets/werkzeug [PACKAGE]
https://github.com/pallets/werkzeug/releases/tag/3.1.4 [WEB]
https://pypi.org/project/werkzeug [PACKAGE]
https://github.com/advisories/GHSA-hgf8-39gv-g3f2 [ADVISORY]